In a radio communication system, in order to perform efficient radio resource scheduling, an evolved NodeB (eNB) must obtain sufficient and accurate downlink channel information. Currently, the information is obtained by means of measurement and reporting performed by user equipment (UE).
The method for measurement and reporting mainly includes: A serving eNB sends certain reference information to a served UE; after receiving a common reference signal (CRS), the served UE calculates and obtains downlink channel information through measurement; and the served UE properly quantizes the measured downlink channel information according to a rule and feeds back the quantized downlink channel information to the eNB.
In addition, a CRS is defined in the prior art for the preceding method.
With the development of radio communication technologies, a coordinated multipoint transmission/reception (CoMP) technology is introduced in the industry. In the CoMP technology, multiple cells that may serve a UE constitute one CoMP set, and the neighboring eNBs to which each of the cells in the CoMP set belongs jointly provide a data transmission service for the UE, so that the UE may obtain higher throughput and raise signal transmission efficiency. In a CoMP scenario, which is different from a conventional scenario where a UE is served by a single cell, the UE needs to measure reference signals sent by multiple eNBs and feed back the downlink channel information that is obtained through measurement to the multiple eNBs.
With reference to the foregoing description, FIG. 1 shows one exemplary radio communication system. This example includes Cell 1, Cell 2, Cell 3, and UE 1, where Cell 1 is a serving cell of UE 1, and Cell 1, Cell 2, and Cell 3 jointly form a CoMP set of UE 1. UE 1 performs a modulo operation according to a Cell 1-ID of the serving cell to calculate and obtain a pilot position of a CRS that is sent by an eNB to which Cell 1 belongs to UE 1, and UE 1 receives, in the CRS position, the CRS sent by the eNB to which Cell 1 belongs, measures and obtains the downlink channel information in Cell 1 according to the CRS, and then properly quantizes and feeds back the downlink channel information to the eNB to which Cell 1 belongs. As shown in FIG. 2, this diagram represents reference signals in a downlink subframe of the eNB to which Cell 1 belongs, where a black block represents a sent CRS, a white block represents a data symbol, and a dashed-line block represents a sent reference signal for another purpose.
According to the foregoing description, the inventor discovers that the prior art has at least the following problems:
1. The UE can calculate and obtain only the CRS pilot position of the cell according to the cell ID of the serving cell, and cannot obtain a CRS pilot position of another cell in the CoMP set, and therefore cannot evaluate the downlink channel information according to a CRS of the another cell.
2. Even if the UE knows an ID of the another cell in the CoMP set, in the current industry, it is stipulated that a downlink pilot position of a cell may be shifted by implicit mapping which binds the pilot position to a cell ID, to ensure that the CRSs of neighboring cells do not collide with each other. However, the shift operation as set forth in the stipulation can ensure only that a CRS has three possibilities of shift, that is, through the CRS, the UE can distinguish only downlink channels of three different cells at most, but a CoMP set generally includes multiple cells that may coordinate in data transmission. In this case, the CRSs of the cells are very likely to collide with each other, resulting in a measurement error of the downlink channels.
3. Even if the CRSs of all cells in a CoMP set are staggered and do not collide, the CRS of each cell may collide with a data symbol sent by another cell. For example, a CRS from Cell 2 collides with a data symbol from Cell 1. Because Cell 2 is a non-serving cell, for UE 1, strength of a downlink channel from Cell 2 is weaker than that from Cell 1. Consequently, the data symbol causes strong interference to the CRS of Cell 2, and UE 1 is unable to correctly measure and obtain the downlink channel from Cell 2 according to the CRS.
In summary, in a CoMP scenario, the method in the prior art is unable to meet a requirement of enabling a UE to receive CRSs sent by eNBs to which multiple cells belong and accurately evaluate and obtain information about multiple downlink channels according to the CRSs.